Dust collector for use with vertically movable dust generators

ABSTRACT

A machine and method for treatment of vertically disposed surfaces of large dimension with dry particulate material comprising means for throwing the dry particulate material at high velocity in the direction toward said surface, a housing enclosing said throwing means having an opening through which the particulate material is thrown against said surface, means for establishing a sealing relationship about said opening between the housing and said surface to confine the particulate material, dirt and dusts within the sealed space, means for collecting the spent particulate material at the bottom portion of the housing and for introducing air into the housing for air washing the spent particulate material to remove dirt and dusts, recycling the washed particulate material for feed to the throwing means, a dust collector for receiving the dirt and dust from within the housing for separation thereof and means for maintaining subatmospheric conditions within the housing to guide the air flow through the housing and about said sealing means to minimize the exhaust of dirt and dust into the atmosphere and in which the support means for said housing includes means for movement of the housing in the vertical direction, means for movement of the housing in the horizontal direction and means for movement of the housing in the direction toward and away from the surface and means for mounting the housing for rocking movement about its pitch and yaw axes to adjust the housing with change in contour of the surface, and sensing means about the opening automatically to adjust the housing for change in contour about the pitch axis and/or the yaw axis and for movement of the housing in the direction towards and away from the surface and for abutting off the feed of particulate material in the absence of a sealing relationship between the housing and surface.

United States Patent [1 1 Primary Examiner-Harold D. WhiteheadAttorney-McDougall, Hersh, Scott & Ladd 'Fogle 1 Jan, 9, 1973 [5 DUSTCOLLECTOR FOR USE WITH S C VERTICALLY MOVABLE DUST A' machini'faia'method" for ireazme'm omrfieany GENERATORS disposed surfaces of largedimension with dry particui late material com risin means for throwinthe dr [7'5] Inventorf James walkerton particulate materi l at l'iighvelocity in the directior l [73] Assignee: The Wheelab'ratorCorporation, toward said surface, a housing enclosing said throwingMishawaka, lnd. means having an opening through which the particulatematerial is thrown a ainst said surface, means for [22] Filed: 1970establishing a sealing rel ationship about said opening [2]] Appl. No.:94,241 between the housing and said surface to confine the particulatematerial, dirt and dusts within the sealed s ace, means for collectinthe s ent articulate Related Apphcat'on Data n iaterial at the bottomportio n of the housillg and for [62] Division of Ser. No. 703,397, Feb.6, 1968, Pat. No. intr ducing air into the housing for air washingthe3,566,543. Y spent particulate material to remove dirt and dusts, I Y irecycling the washed particulate material for feed to [52] U.S. C1...51/273 the throwing s, a dust ll t r for r iving the [51] Int. Cl. .L..B24b 55/06 dirt and dust from Within the housing for Separation 5811mmof Search ..285/61; 15/302;51/9,273 thereof and means for maintainingsubatmospherict 1 conditions within the housing to guide the air flowthrough the housing and about said sealing means to [56] ReferencesCited minimize the exhaust of dirt and dust into the at- Q mosphere andin which the support means for said UNITED STATES PATENTS housingincludes means for movement of the housing 1 990,318 2 1935 Dabe ..s1 9the vertical direction movement of the 3:034262 5/1962 Pawlson 51/9housing ,in the horizontal direct on and means for 3,262,228 7/1966Schenckm movement of the housing in the direction toward and 3,274,8929/1966 cameww; "WM/273 x away from the surface and means for mountingthe 2,634,560 4/1953 Ramm ..51 273 housing for rocking movement aboutits Pitch and y axes to adjust the housing with change in contour of thesurface, and sensing means about the opening au- FOREIGN PATENTS 0RAPPLICATIONS tomaticall to ad'ust the housin for change in contour aboulthe pllch axls and/or the yaw axis and for 846,217 7/1949 Germany ..5l/9

movement of the housing in the direction towards and away from thesurface and for abutting off the feed of particulate material in theabsence of a sealing relationship between the housing and surface.

3 Claims, 11 Drawing Figures PAIENIEDJAN 9 ms SHEET 1 [IF 8 FIG.- 1

PATENTEDJAN 9l973 3; Y Y sum um 8 708826 DUST COLLECTOR Fonusr: WI'IHVERTICALLY I MOVABLE DUST GENERATORS This application is a division ofmy copending application Ser. No. 703,397, filed Feb. 6, 1968 andentitled Machine for Treatment of LargeVertical Surfaces, now U.S. Pat.No. 3,566,543, issued Mar. 2, 1971.

This invention relates to the treatment of surfaces of verticallydisposed walls of large dimension, such as the outer side wallsof aships hull, large conservation tanks for water, gas and the like fluidmaterials, or other paneled structures, and it relates more particularlyto a method and means for cleaning such vertically disposed paneledstructures or walls with dry particulate abrasive materials blasted ontothe surface.

To the present such surfaces or walls are air blasted with crushed slagas the abrasive. Such abrasive particles breakdown so rapidly that noattempts are made for recovery and the abrasive is wasted after thesingle use. The described cleaning process is subject to a number ofdrawbacks including high cost by reason of the high cost of thecompressed air that is required; the slow rate of cleaning; the need forthree men for operation of a single cleaning head; the high cost forhandling large amounts of abrasive; the labor and equipment required toremove the abrasive; and the need to dispose of the large amount ofspent abrasive that is continuously being generated.

Aside from the above disadvantages, the process presently employed ischaracterized as a dirtyprocess which raises excessive amounts of dustand additional means are therefore required to protect personnel on theship.

It is an object of this invention to provide a dust collector forusewith means for surface treatment of vertical panels'and walls oflarge dimension by blasting with dry particulate material. I These andother objects and advantages of this invention willhereinafter appearand, for purposesof illustration, but not of limitation, an embodimentof the invention is shown in the accompanying drawings in which FIG. 1is a perspective view in elevation ofa machine embodying the features ofthis invention; I 1 FIG. 2 is a perspective view in side elevation ofthe blasting head alongsidea wall to be treated; I

FIG. 3 is an enlarged perspective view in rear elevation of the blastinghead and supports;

FIG. 4 is a front elevational view of the blasting head and associatedelements;

FIG. 5 is aside elevational view partially in section of the blastingchamber and abrasive handling parts;

FIG. 6. is a schematic elevated. view of the various frame members forsupport of the blasting chamber;

FIG. 7 is a view similar to that'of FIG. 6 showing the arrangement ofelements for movement of the blasting head in theforward andrearward-direction relative the supporting frames;

7 FIG. '8 is aview schematically showingthe'arrangement of elements forangular adjustment of the blasting FIG. 9. is anelevationalview-partially in section of I the duct'communicating theblast chamber with the dust collector;

FIG. 10 is a sectional view taken alongline 10-10 of F IG. 9; and

' FIG. 11 is an electrical diagram for the machine;

Invention will hereinafter be described with reference to a machine forcleaning the outer surfaces of a shipshull with dry particulate materialblasted onto the surface of the hull by a centrifugal wheel in anassembly which can be moved about the hull in'a manner to accommodatethe various curvatures of the ships hull for substantially uniformcomplete coverage thereof It will be apparent from the description thatthe machine and method of this invention can be employed equally wellfor the cleaning or otherwise treating of the vertically disposed wallsof outside storage or conservation tanks of large capacity or othervertically disposed walls of metal or the like paneled structures.

The machine of this invention makes use of a single blasting head 10which includes a blast chamber 12 having an opening 14 at its forwardend which may be of various configurations but which is preferably ofoval or rectangular shape with the major length of the openingperpendicular to the. axis of the bladed centrifugal throwing wheel 16mounted for rotational movement. within the base of the chamber 12for-turning movementabout a vertical axis. Centrifugal blastingwheels ofthe type described are manufacturedand sold by The WheelabratorCorporation of Mishawaka, Ind., under the trade name WHEELABRATOR" andare more specifically described inU. S.;Iats. Nos.

2,708,814 and 2,819,562. Suffice it'tosay that such throwing wheelscomprise a plurality of radially extending blades arranged incircumferentially spaced apart relation between confining disc plateswith means 'for feeding particulate treating material, such as steelshot, steel grit or the like-onto the innerends of theblades wherebysuch particulate material is thrown centrifu gally at high velocity fromthe outer ends of theblades as the wheel is rotated at highspeed aboutits axis by the driving motor 18. The particulate material is thrownforwardly from the ends of the blades through the open end of the blasthousing into engagement with the'surface facing the blast housing.

For this purpose, a large flanged plate 20 is secured to the open edgeof the blast chamber and inner and outer sealing members 22 and 24,formed of resilient or rubber-like material such as polyurethane, and offrusto-conical shape, are secured to extend continuously about the blastopening 14 withthe rearward ends of the sealing members secured to theflanged plate 20 to provide a spacedrelationship therebetween. Theresilient sealing members 22-'-and 24 areprotected from the abrasivethrown outwardly from the wheel by a baffle' plate 26- which is securedto the flanged plate 20 inwardly of the inner sealing member 22 andarranged to, project angularly outwardly between and sealing member.'andthe interior. of the blast chamber for a distance to correspond withthe in-- nermost reach of thesealingmembers. I 1 a The sealingmembers'22 and 24 are adapted to engage the surface to be treatedimmediately adjacent the blast area and means are providedforsealingengagement in a manner to deflect the forward edge portions of thesealing members when the blasting head is in proper position of usethereby to effect a sealing relation'ship between the blast chamber andthe surface.

Air' inlet spaces 30 encircle the upper end portion of the blast chamberand communicate with the space between the inner and outer sealingmembers 22 and 24 through openings 32 whereby air under pressure theslot 38 in the flanged plate at the base of the inner sealing member 22or over the deflector plate 26 and the shed plates '40 at the bottom ofthe blast chamber. The blasting head is provided with an air inlet 42immediately below the shed plates 40, 44,46 and 48 for-theintrodu'ctionof air which passes upwardly about the. inner ends v of the shed platesand through the descending curtain of spentiabrasive anddust to air washthe abrasive and remove dust and fines from the spent abrasive For thispurpose,theshed plates 40, 44-,

46 and 48 comprise verticallyspaced apart downwardly angled plateshaving their inner edges in i overlapping .relations'hipto provide acascade of the the wholeassembly. By the described arrangement of airflow, it becomes possible "to operate the blasting head continuously forhours with little, if any, heat build-up in the abrasive. v I v The sidewalls 50 of the blast housing below the blasting head converge angularlyinwardly in the direction towardseach other to define a collecting chutethrough iwhich'the air washed abrasive and air separated particles fallgravitationally into a trough 52 at the bottom having a screw 54rotatably mounted therein for'displacernent of the collected particulatematerial rearwardly'for'movement over a perforated.

plate or screen 56, which forms a part of the bottom wall of theconveyor and through which the reusable abrasive-particles pass whilethe larger particles of paint, rust, scaleand the-like are displacedover the surfaceyof the screen to a discharge chute 58'comminicating'withthefar, end 'of the screen for discharge as waste. 1 I

'Theabrasiveparticles which pass" through the perforated plate or-screen56 are returned as feed forthe v centrifugal throwing wheel. For thispurpose, a trough 60 is providedbeneath the perforated'plateforcollection of the abrasive particles passingfthrough the screen. Aconveyor returns the abrasive particles collected in the 'trough to thefeed'hopper62 abovethe blast chamber. Various conveyors or elevatormeans may be employed for lifting the abrasive particles to the feedhopper; In the preferred practice of this invention,

'blast chamberwith the-collector. i

it is desirable to make use of a means in which a substantial sealedrelationship can be maintained in the conveyor means to minimize theflow of air there'thro'ugh in response to the suction generated in theblast chamber by the dust collector, which will hereinafter bedescribed.

One such elevator means illustrated in the drawings comprises a tubeelevator whichl ma'kes' use of a continuous length of rigid tubing 63which encircles the blast assembly. A link'chain 64 extends continuouslythrough the interior of the rigid tubing and spaced links are providedwith disc members 66 which function in the manner of a piston head tosweep the abrasive particles in advance thereof through the tube. Suchdisc members are preferably formed of relatively rigid material, such aspolyurethane discs, which are capable of sealing engagement with thesurrounding wall of the tubing with minimum frictional resistance topermit linear displacement with the link chain without excessive work.

The portion of the tubing underlying the trough is cut away to providean opening 68 through which the abrasive particles will fall from thetrough into the tubular conveyor and into the path of the disc members.

Similarly, the portion of the tubing overlying the hopper 62 is alsoprovided with an opening 70 toenable the raised abrasive particles tofall from the tubing into the hopper. Means for continuous displacementof the link chain is provided beyond the delivery opening in the form ofan electrical motor 72 connected to a suitable speed reducer 74 having asprocket on the end thereof fastened operatively to engage alternatelinks ofthe chain. v 5 I The-feed hopper 62 is mounted above the wheel.16 for feeding abrasive particles to the inner ends of the blades ofthe rotating wheel which throws the abrasive particles centrifugallyfrom the ends of the blades in the direction toward the opening 14 inthe blast head onto the facing surface to be processed. A valve 76, suchas an electromagnetic valve, is interposed in the feed line 78 betweenthe hopper and thewheel to control the flow rate of the shot, gritofotherabrasive particles to the wheel. The hopper is provided with asensing means 80, such as a switchm'eans extending through the sidewallinto a lower portion of the hopper to shut the valve when the levelof abrasive falls below the sensing means in the hopper.

In operation with the sealing strips 22 and 24in seal ing engagementwith the surface to effect a substantially sealed relationship betweenthe blasting head and said surface, subatmospheric conditions can bemaintained within the head to effect the described directional flow ofair about the sealing strips and for air washing the spent abrasiveaswell as to carry off the collector which communicates with theinterior of the blasting head whereby suchsubatmospheric conditions aremaintained simultaneously with the effective removal of dust entrainedwith the air traveling through the blastchamber thereby to prevent'theiss'uanceof suchdust and dirt into the atmosphere'. Use can be made of-adust collector of the conventional type with ducts 82 connecting theoutlets 84 at the top-of the Special means are interposed between theducts and the dust collector to permit the various movementsof the blastchamber hereinafter to be described to enable the blast head to conformwith the contour of the surface being cleaned and for movement of theblast chamber over the surface for coverage of the surface during thecleaning operation. Such special connection means for a movable head isbelieved to constitute a new and novel construction which may bedescribed and claimed in a separate application but which will alsohereinafter be described to complete the description of the machine.

Having described the basic elements of the blast head and the operationthereof, description will now be made with respect to the mounting ofthe head on suitable supports for movement of the head vertically tocover a-verticalsection of the surfaceand laterally for coverage of awidth of surface as well as movement in the direction toward and awayfrom the surface to achieve the desired sealing engagement with thesurface during the operation. The blast head'will also be gimbal mountedfor rocking movement about a vertical yaw axis as well as horizontalabout a pitch axis to conform the head to change in surface'contour inthe vertical direction as well as in the horizontal direction and withmeans operative automatically or manually-to effect such'movements inresponse to changes in contour or curvature and tomaintain the pressurecontact between the head'and surface sufficient to deflect the ends ofthe sealing members 22 and 24 to maintain the desired sealingrelationship.

The described assembly, including the blast chamber, spent abrasivecollector, hopper and elevator are mounted for movement together in thevertical, lateral, forward I and rearward directions on suitable frameand guide members including a tower 90 formed of four spaced masts orcolumns 92, 94, 96 and 98. The tower is preferably adapted to beshiftable alongside the wall for positioning. the blast chamberoperatively to engage additional increments of the wall surface fortreatment. This semi-stationary tower would-normally be stationaryduring the time the blast head is in operation, but it would be capableof being moved intermittently to a newposition alongside the worksurface by means of a barge, tracked vehicle'or otherwise. A main frame100 in theform of a rectangularly shaped section formed of a pair ofvertically disposed laterally spaced apart angle members. 102 and 104and a pair of horizontally disposed vertically spaced apart anglemembers 106 and 108, joined one to the other at their outer ends, ismounted for guided up and down move ment between the fixed'masts 92, 94,96 and 98. For thispurpose, the side members 102 and 104 supportvertically spaced apart guide rollers .110 extending laterallyinto'operative engagement inside tracks 112 providedon the innersurfaces of the masts to guide the main frame during movementverticallyrelative to the main frame. The rollers 110 are mounted forfree rotamounted for free rotational movement on a spindle supported atits ends between the masts at a level above the upper limit of travel ofthe main frame. The chain is connected at one end to the center of theupper crosswise extending angle member 106 of the main frame while theother free end, which depends from the sprocket wheel 118, supports acounterbalance 120 for the main frame and the elements supportedthereby. Motor means,not shown, are provided for movement of the chainto raise and lower the main frame. It will be apparent that other-meansfor elevating and lowering the main frame relative to the supportingmasts may be employed and that the vertical travel of the main framerelative to the masts will depend somewhat upon the length ,of themasts. In a practical modification, the masts are dimensioned to enablevertical movementof the main frame for a distance within the range of 30to feet. Means other than the tower and fixed masts can also be used tosupport and provide vertical movement of the main frame and assembly.For example, the main frame and assembly could be supported and movedvertically by means of overhead cables, cranes, telescoping supports orother means. An'inner frame 130 is adapted to be supported on the mainframe for sidewise movement relative thereto. Such inner frame comprisesa rectangular section formed of interconnected, laterally spaced apart,vertically disposed channel members 132 and 134 and horizontally spacedapart upper and lower crosswise extending channel members 136 and 138. Iv Laterally spaced apart rollers'140 mounted for rotational movement onthe upper and lower, horizontally disposed main frame members areadapted to be received in guiderails 142 on the underside of thechannels 136 and 138 of the inner frame members to permit theinner framemember to move laterally relative to the main frame member 100 to theextentpermitted by the portions of the mainframe between the fixedmasts. Thus the extent of lateral movement of the inner'frame will besomewhat less than'the amount of vertical movementof the main frame. Inthe illustratedmodification, a lateral travel of about 4 to 10 feet canbe easily designed into theunit. Thus the inner frame 130 is capable ofvertical and sidewise movement relative to the fixed m asts. I

Lateral movement of the inner frame 130 relative the main frame 100 isadapted to be effected by means of a pressure fluid'operated piston andcylinder assembly in which the end of the piston 144 is anchored toeither the main frame 100 or the inner frame 130 while the base of thecylinder 146 is anchored to the other of the frame members with thepiston and cylinder extending horizontally to effect lateraldisplacement of the inner frame relative the main frame. It will beapparent that the desired relative displacement between the framemembers such as a horizontallydisposed rack secured to the inner framein operative engagement with a motor operated pinion gear supported bytheother frame with the pinion in engagement with the rack to .effectrelative lateral movement of the inner frame to the main frame inresponse to motor operation of the gear in one'direction or'the other. aI

The inner frame 130'independently supports a head frame 150 in a mannerto permit forward and backward movementrelative to the inner frame andthe main H 7 frame and masts in the direction toward and away from thesurface to be cleaned. As illustrated in FIG.- 6, the

130'are laterally spaced by an amount to receive the head framesupporting the blast therebetween. Secured to each of the inner edges ofthe laterally spaced apart vertical channel. members 132 and 134 are apair of longitudinally disposed, inwardly platforms or rails 158 resideadjacent the-bottom side of thelower plat forms 1'53 toestablish aguided-support for the" head frame while permitting movementof the headframe horizontally in a direction perpendicular to the inner frarne. 1HMeans are schematically illustrated in FIG. '7 of the drawingsforactuation of the head frame for movement relative the. inner frame. Asillustrated in the drawings,

chamber 7 side channel members 132 vand 134 of the inner frame 7 8offset portion of the yoke, extends rearwardly for operation of afour-way valve 180 mounted on the head frame;

Change in surface contour will react through the rollers to cause theyoke to rock about its pivot'with cor? responding displacement of thearm 178 in one direction orthe other depending upon the change of angleof the yoke. Rocking movement of theyoke about its pivot in theclockwise direction will operate to 1 laterally spaced apart arms 192and 194 which extend one suchi means comprises another pressure fluidoperated piston andcylinder assembly in which the end of the piston 160is pivotally attached to a-portion of the head frame 150 while the baseof the cylinder 162 is pivotally attached to a rearward portion on theinner 7 frame 130. Pivotal means for attachment are employed to enablethe gimbalrmounting of the blast chamber for rocking movement about itsvertical and horiaontal axes relative the supporting'framesl T it willbe understood that other conventional means matic'ally to' adjust thehead in the'direction toward and away fromgthe surface being cleaned forequalizing pressure on the sea ls'in' amanner to maintain the desiredscaling relation between the sealing members and the surface.

In the illustrated mbdificatiomthe means-for adjust-. ment of theheadabout its pitch axis allows for change in the'con'tour of the'ships hullin the vertical direction.

In the illustrated. modification, such means comprises a yoke 170 oneach side of the head pivoted at its center on pivot pins .172 rigidwith the sidewall of the blast chamber for free rocking movementrelativethe hous ing about the pitch axis. Casters 174, in the formofrubber rollers, are rotatably. mounted on the'vertically spaced, apartends of the yoke in position to extend for .wardly of the face of theblast head into rolling engagement withvertically'spaced apart portionsof the surface 116 being'treated, when the blast-head is in properpositionof use. An arm 178; pivoted at one end onto an the pitchaxis'and about the-yaw'axis as well as autodescribed;

alongside the blast housing with pivot pins for trunnions.196 extendinginwardly. into engagement with bearings on the sidewalls of theblast'housing pivotally to mount the blast housing for rocking movement;This the-blast housing of the blasting head is capable 'ofrocking-movement about its horizontal axis relative the.

head frame. Rocking movement :of the blasting head relative the headframe is effected by a pressure fluid operated .piston and cylinderassembly with the cylinder 198 anchored at the far end to the yoke-190while the piston 200 is pivotallysecured at its free end to a portion ofthe head vertically offset. from the pivotal axis. The piston andcylinder are controlled .by the four-way valve 180 for operation in onedirection or the other for angular adjustment of the'head. .For pivotalsupport of the head for rocking move-. ment-about'the yaw'axis, the headandyoke are supported as a unit on a vertically disposed shaft 196 whichextends through a vertically aligned opening through the center of-theyoke 19.0 thereby-to mount the yoke for-rocking movement abouttheshaftasthe yaw axis. Angular adjustment of the yoke and head about theshaft is, effected by apressurc fluid operated piston and cylinderassembly 202 having the cylinder 204 pivotally secured .onto a bracket206 rigid with the head frame 150' while the piston 208 is pivotallysecured'to a portion of the yoke190 l aterally offset from the yaw axis194. i

As-illustrated in FIG. 6, the entire head assembly which now includestheblasting head, thefyoke 190, in which the blasting 'head is mountedfor rocking movement about the pitch axis, and the head frame 150 onwhich the yoke 190 is mountedifor rocking movement about the yaw axis,is supported on the rollers-140for relative movement injthc directiontoward and away from the surface to be treated by the pressure fluidpiston and cylinder assembly 1 60-162 as previously Rocking movement ofthe head'about its' yaw axis and endwise positioning of the head forsealing engagement with the surface is controlled by a pair ofproximisensingmerhbers are capable of 210 as one or the other losescontact with the surface by reason of change in surface contour.

The laterally spaced apart sensing heads also operate switch means foractuation of the piston and cylinder assembly 160-2 between the innerframe 130 and the head frame 150 for adjustment of the head frame andblasting head in the direction toward and away from the surface inresponse to operative pressure between the surface and the sensingmembers therebyautomatically to adjust the head for the desired pressurecontact with the surface.

The laterally spaced apart sensing members can also operate throughsuitable means to close the valve '76 and shut down the flow of abrasiveto the throwing wheel responsive to loss of contact between both of thesensing members and the surface thereby to indicate complete separationbetween the surface and head and loss of the desired sealingrelationship therebetween.

It will be understood that the controls achieved by the rollers 156 canbe embodied in thesensing members thereby to enable elimination of therollers and supporting structure. Under such circumstances,

. sensing members could be arranged in vertically spaced relation aswell as in laterally spaced apart relation to detect changes incurvature or angle of the wall while at the same time sensing sealingengagement with the wall.

The main frame also supports a horizontally disposed platform 220 onwhich an operator may stand for vertical movement alongside the blastinghead and a control panel 222 alongside the platform with control buttonsfor l the various operations under. the control of the operator. A 7

While the dust collector can be mounted on the main frame for verticalmovement with the blasting head,it is preferred separately andstationarily to mount the dust collector as a unit separate and apartfrom the main frame, especially when the collector is of the dust tubetype. When use is made of a separately supported stationary dustcollector for use with a vertically movable dust generator, such as thedescribed blast assembly, long expandable ductwork of the telescopingtype is required in order to maintain proper communication between thedust collector and generator. Ductwork ofthis type is incorporated witha large number of problems as well as high cost. A new and novel conceptfor communication between a vertically movable dust generator and astationary dust collector or separator has been developed nicating thelongitudinally movable dust generator or iii blast housing with thestationary dust collector 230 comprises an elongate, vertically disposedrigid duct 232 of rectangular, triangular, or polygonal shape, having anopen outer wall 234 which is covered throughout its length by a flat,flexible or rubberlike belt 236 dimensioned to have a length slightlygreater than the length of the opening and a width slightly greater thanthe width of the opening so that the lateral edge portions of the beltwill overlap flanged edge portions extending inwardly a short distanceinto the opening from the side edges of the adjacent side walls of theduct. The upper and lower end portions of the belt236 are fixed to theduct with the opening in the duct dimensioned to have a lengthcorresponding to the vertical travel of the main frame. Box 240 havingupper and lower walls 242 and 246 converging to form a V-sectiontherebetween and enclosed by side walls 248 and 250, is mounted forvertical sliding movement with the main frame while in engagement withthe open side of the duct in substantially sealing engagement therewithso that the open side of the V-shaped box faces the open side of theduct for complete communication therebetween. I

The box is dimensioned to'have a width corresponding to the width of'theopen wall of the duct with the spaced relationship between the sidewalls 248 and 250 corresponding to the width of the belt. I

Within the box an upper and a lower roll 252 and 254 respectively aremounted for free rotational movement in the upper and lower ends of thebox and a third roller 256 is mounted for free rotational movement atthe apex of the V-shapedbo'x section. Betweenthe upper roller 254 andthe roller 256 at the apex, there is provided a rigid guide plate 258,secured at its lateral edges to the side walls of the box. The guideplateextends from the upper roll 252 to the center roll 256 from a pointspaced a short distance below the lower periphery of the upper roll 252toa tangency with the upper periphery of the center roll 256 Anothersimilar guide plate 260 extends from a tangency with the lower peripheryof the center roll 256 to a point spaced upwardly a short distance fromthe upper periphery of the lower roll 254.

In its mounted relationship, the rubber-like belt 236 extends into thebox about the lower periphery of the upper roll 252 over the upper guideplate 258 to the rear of the box over the center roller 256 and thenunder the lower guide plate 260 to the lower roll 254. Thus the belt isdeflected from the duct throughout the length between the upper andlower rollers 252 and 254 of the box to enable communication between thebox and the duct while maintaining asealed relationship therebetweenindependently of the vertical position of the box relative the duct.Thus the flat rubber belt 236 coversthe open side of the duct throughoutthe entire length of the opening except the area the guide plates forguided support during travel through the box and about the rollers andto assist such guided support, it is desirable to form the ends'of thesupporting plates 258 and 260 with curvilinear lips 262.

An opening 264 is provided in a side wall of the box I and the flexibletubing 82connects the inlet opening 264 with theoutlet openings 84 inthe upper wall of the blast chamber. Another opening is provided in oneof the side walls. of the vertical duct and tubing or other meanscommunicates the outlet opening of the duct with'the inlet opening tothe dust collector 230.

Suction from the dust collector operates to hold the flat belt 236 insubstantial sealing engagement at its lateral edges with the duct 232.The box is connected to the main frame for movement vertically relativethe duct with the blast assembly. Thus as the assembly moves-up and'downthe masts, the box 240 moves with the assembly relative the duct and thebelt is displaced awayfrom the wall through the length covered by thebox.

Various means may be provided for guiding the box 240 in sealingengagement between the lateral edges of the duct. One such meanscomprises spaced flanges of the lateral edges of the side walls of thebox to define a recessed portion therebetween in which the flangeportions extending inwardlyfrom the side walls of the duct are receivedin sliding engagement. It will be understood that the vertical duct'canbe of triangular or other polygonal shapes and that other means, may be12 and the surface becomes broken thereby to avoid loss of abrasive orthe exhaust of dirt and dust intothe atmei'gjhere.

ile the sealed relationship is maintained between the head and thesurface, spent abrasive is recovered for use and dirt and dusts arewithdrawn from within the chamber for separation without being exhaustedinto the atmosphere. 1

Thus a continuous operation is achieved which permits efficient andeconomical use to be made of more expensive. and reusable abrasive, andvwithout loss of abrasive or exhaust of dust and dirt into theatmosphere. A much quieter operationis provided by reason of the sealthat is maintained about the area being worked.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation without departing from thespirit of the invention, especially as defined in the following claims.

provided for sliding. engagement of the box relative the open side ofthe duct.

In operation, the main frame is raised to the desired level alongsidethe surface to be cleaned. The head frame-is then displaced forwardlyuntil the desired sealvhag-engagement is established between the sealingmembers and the surface andthereafter the abrasive material is meteredby the valve .76 for flow from the feed hopper 62 to the throwing wheel.

The wheel throws the abrasive forwardly at high velocity through thehead opening onto the work surface and the spent abrasive fallsgravitationally downwardly over the shed plates 40-48 to the bottom ofthe housing for'linear displacement bylthe screw 54 over the screenmember 56. The reusable abrasive particles which pass through the screenare returned to the hopperby the tube elevator.

The suction from the dust collector causes air to be drawn into theblast housing for flow upwardly over the ends of the shed plates to airwash the abrasive falling from .theends of the plates whereby thedustsand dirt are removed from within the housing through the. outlets 84 tothe dust collector.

While continuing to operate, the head can be moved up or down by thelift chain .116 to coververtical sec-. tionsof the surface and it can bemoved laterallyfor covering an area ofthe surface without readjustment,of the entire assembly. After blast cleaning a vertical section, of thesurface, ,the blasting operation can be stopped and the tower with theentire vassembly moved to a new location for blasting another verticalsection.

The guiderollers and the sensing members operate automatically to adjustthe head angularlyabout its horizontal or. vertical axis to conform thehead to any change in contour of the surface. The sensing memberslclaim: 1 1 1 1. In an assembly which makes usev of a dust generatorhaving vertical movement and a stationary dust collector, meansinterconnecting the vertically movable dust generator withthe dustcollector in amanner to establish a substantially scaling relationshiptherebetween comprising a vertically disposed duct having an'open sidedimensioned to have a length cor responding to the length of verticalmovement of the dust generating means, a belt of resilient materialcovering said open side without attachment thereto throughoutvthe lengthcorresponding to the length of travel of the dust generating means, ahead boxmovable .with said dust generating means in a verticaldirection'and having an open side in facing relation with the open sideof the duct and with sidewalls of said headbox being spaced tocorrespond with the open side'of the duct and to receive the belttherein, deflector means within the headbox over which the belt travelsto deflect the belt in the direction away from the open side of theductin' at least a portion of the area covered bythe head box to providedirect 'communicationbetween the interior of the head box and-the duct,conduit means communicating the interior of .the head box with the dustgenerator, other con duit means communicating the interior of the ductwith the dust collector and ,means for generating subatm'osphericconditions. within the duct constantly to urge the belt into sealingengagement with the portion of the duct not covered by the head box. r

2. 'A device as claimed in claim 1 in which rollers'aremountedwithin'the head box for free rotational movement about axes whichdefinethe vertices of a triangle with two of the rollers adjacent theopen side and in which the belt passes through' the head .box about theinner peripheral portions of the pair of rollers and about the outerperipheral portion of the roller in between to guide the b elt in atriangular path through th eheadbox'. I

3. Adevice as claimed in claim 2 which includes "a guide plate extendingfrom the upperof the pair of rollers to the intermediate roller and fromthe intermediate roller to the lower of the pair of rollersto supportthe portions of the belt between the rollers.

1. In an assembly which makes use of a dust generator having verticalmovement and a stationary dust collector, means interconnecting thevertically movable dust generator with the dust collector in a manner toestablish a substantially scaling relationship therebetween comprising avertically disposed duct having an open side dimensioned to have alength corresponding to the length of vertical movement of the dustgenerating means, a belt of resilient material covering said open sidewithout attachment thereto throughout the length corresponding to thelength of travel of the dust generating means, a head box movable withsaid dust generating means in a vertical direction and having an openside in facing relation with the open side of the duct and with sidewalls of said head box being spaced to correspond with the open side ofthe duct and to receive the belt therein, deflector means within thehead box over which the belt travels to deflect the belt in thedirection away from the open side of the duct in at least a portion ofthe area covered by the head box to provide direct communication betweenthe interior of the head box and the duct, conduit means communicatingthe interior of the head box with the dust generator, other conduitmeans communicating the interior of the duct with the dust collector andmeans for generating subatmospheric conditions within the ductconstantly to urge the belt into sealing engagement with the portion ofthe duct not covered by the head box.
 2. A device as claimed in claim 1in which rollers are mounted within the head box for free rotationalmovement about axes which define the vertices of a triangle with two ofthe rollers adjacent the open side and in which the belt passes throughthe head box about the inner peripheral portions of the pair of rollersand about the outer peripheral portion of the roller in between to guidethe belt in a triangular path through the head box.
 3. A device asclaimed in claim 2 which includes a guide plate extending from the upperof the pair of rollers to the intermediate roller and from theintermediate roller to the lower of the pair of rollers to support theportions of the belt between the rollers.